I. Field of the Invention
The present invention relates generally to a withdrawal device for use with a cryogenic tank.
II. Description of Related Art
Cryogenic tanks of the type designed to contain extremely cold liquids, such as liquid nitrogen, typically include a neck at the top of the tank. This neck has an interior throughbore open to the interior of the tank. Such cryogenic tanks are used in many applications, such as cryosurgery. When used in such applications, however, it is frequently necessary to withdraw a relatively small portion of the liquid from the tank using a withdrawal device.
There have been a number of previously known withdrawal devices for use with cryogenic tanks. These previously known devices typically comprise a housing having a flange which is adapted to abut against the top of the neck of the cryogenic tank. An elongated extraction tube then extends both through the housing and into the interior of the cryogenic tank as well as exteriorly of the cryogenic tank. With the housing secured to the neck, pressure caused by vaporization of the cryogenic liquid within the tank forces the cryogenic liquid out through the extraction tube and exteriorly of the cryogenic tank. Typically, a manually operated valve is fluidly connected in series with the extraction tube.
In order to fluidly seal the housing to the cryogenic tank, these previously known withdrawal devices typically include an annular seal having one end in abutment with the housing flange and dimensioned for insertion into the neck opening. A circular seal support supports the other end of the annular seal while a rod secured to the seal support extends upwardly through the flange. A nut then engages a threaded portion on the rod so that rotation of the nut axially compresses the seal and expands the seal radially outwardly into sealing engagement with the interior surface of the neck opening. This nut is oftentimes positioned at the base of the housing and just above the flange.
These previously known withdrawal devices, however, have not proven wholly satisfactory in use. One disadvantage of these previously known devices is that many require the use of a separate tool, such as a wrench, in order to tighten the annular seal into sealing engagement with the cryogenic tank. Still other previously known withdrawal devices include outwardly extending arms secured to the nut which permit the nut to be manually rotated. In either case, however, tightening of the nut is difficult to achieve.
A still further disadvantage of these previously known withdrawal devices is that the number of rotations of the nut, and therefore the axial compression of the seal, is unlimited. In many cases, over tightening of the nut results in over compression of the seal thus damaging the seal. When this occurs, it is necessary to repair the withdrawal device by replacing the seal with a new seal.
The present invention provides a withdrawal device for a cryogenic tank which overcomes all of the above-mentioned disadvantages of the previously known devices.
In brief, the device of the present invention comprises a housing having a flange adapted to overlie and abut against the top of the neck of the cryogenic tank. An extraction tube has a first portion adapted to extend through the flange and into the interior of the tank. The extraction tube also includes a second portion which extends laterally outwardly from the housing and a fluid valve is fluidly connected in series with the second portion of the tube.
In order to fluidly seal the housing to the neck opening of the cryogenic tube, the withdrawal device of the present invention includes an annular seal having one axial end in abutment with the flange. A circular seal support overlies and supports the opposite end of the seal. Both the seal support and seal are dimensioned for insertion into the neck opening.
In order to axially compress the annular seal so that the seal expands radially outwardly, an elongated rod has one end secured to the seal support while its other end extends through the flange and housing so that the opposite end of the rod extends through the top of the housing. This second end of the rod, furthermore, is externally threaded.
A lever includes a nut at one end adapted to threadably engage the second or upper end of the rod. Consequently, with the lever nut threadably engaged with the upper rod end, rotation of the lever compresses the annular seal between the flange and the seal support thus expanding the seal radially outwardly into sealing engagement with the interior surface of the cryogenic tank neck.
Unlike the previously known devices, however, the second end of the rod is positioned within a recess in the lever so that the second end of the rod is aligned with a closed wall portion in the lever. Since the second end of the rod is positioned within the recess, the number of axial rotations of the lever, and thus the axial travel of the rod, is limited thereby preventing over tightening of the rod and over compression of the seal.